1. Field of the Invention
The present invention relates to a kneader for kneading a material to be kneaded such as resin.
2. Description of the Related Art
Heretofore there has been known a twin-screw extrusion type kneader for kneading a material to be kneaded such as resin. Such a kneader includes a pair of screws disposed in parallel with each other and a barrel having in the interior thereof a kneading space for accommodating both screws. The kneading space of the barrel has a shape such that a pair of accommodating spaces of a substantially circular section for accommodating each of the screws respectively are connected together so as to overlap each other partially in a radial direction. In this conventional kneader, the pair of screws are each rotated about the axis thereof, and thereby a material to be kneaded which is introduced into the kneading space is kneaded by utilizing a shear force developed between both screws and also between each screw and an inner wall surface of the barrel.
In such a kneader, each screw undergoes pressure from the material to be kneaded during kneading of the material. This pressure sometimes results in a case where each screw undergoes an unbalanced load in a specific direction orthogonal to an axial direction of the screws and causes a deflection. Once there occurs such a deflection of each screw, there is a fear that the outermost periphery portion of each screw may contact the inner wall surface of the barrel, with consequent wear of both screw and barrel. Thus, there arise the problem that the life of each screw and that of the barrel become shorter due to such wear and the problem that metal powders resulting from the wear are mixed as foreign matters into the material being kneaded, resulting in the quality of the material being deteriorated.
Techniques for solving the above-mentioned problems are proposed in the following Patent Literatures 1 and 2.
In Patent Literature 1 there is disclosed a technique of forming a screw in a shape such that the angle of a front face in a rotational direction of the screw is set smaller than in an ordinary type of a screw, thereby making the pressure which the screw undergoes from a material to be kneaded difficult to increase and thereby diminishing deflection of the screw caused the above pressure. According to this technique, the wear induced by contact of the screw with the inner wall surface of the barrel is diminished.
In Patent Literature 2 there is disclosed a technique of applying a surface treatment to the surface of each screw and an inner wall surface of a barrel to improve wear resistance of those surfaces, thereby diminishing wear induced by contact of the screw with the inner wall surface of the barrel.
[Patent Literatures]
1. Japanese Patent Laid-Open Publication No. 2004-262177
2. Japanese Patent Laid-Open Publication No. Hei 9 (1997)-85739